HRSGs: Heat Recovery Steam Generators

Imagine finishing a hot shower and, instead of simply letting all that leftover steam vent uselessly out of the bathroom, rerouting it to also warm the room next door, capturing heat that would otherwise be thrown away entirely rather than generating it fresh. A Heat Recovery Steam Generator, HRSG, does exactly this inside a power plant, capturing the very hot exhaust gas leaving a gas turbine, covered elsewhere on this site, gas that would otherwise simply vent into the atmosphere still carrying enormous unused heat, and using it to boil water into steam.

That steam is then fed into a steam turbine, covered elsewhere on this site, generating a second stream of electricity from heat that a gas-turbine-only plant would have wasted entirely, which is the actual mechanism behind the term combined cycle, and the reason a combined-cycle plant meaningfully outperforms a simple-cycle gas turbine plant on fuel efficiency per unit of electricity produced.

Because an HRSG's entire purpose depends on sitting directly downstream of a specific gas turbine model's exhaust characteristics, HRSGs are usually engineered and ordered as a matched pair with the turbine feeding them, which means HRSG delivery queues are effectively coupled to, and compounded by, the same multi-year gas turbine order backlog covered elsewhere on this site, a data centre developer choosing the more fuel-efficient combined-cycle route is not just waiting on a turbine, but on a turbine and a matched HRSG arriving together.

This is why combined-cycle configurations, despite their genuine efficiency advantage, have remained a comparatively small share of the on-site power solutions data centre developers are actually deploying today, when reciprocating engines and aeroderivative turbines, both covered elsewhere on this site, can be installed in a fraction of the time a full combined-cycle gas turbine and HRSG pairing currently requires.